Aortopulmonary (AP) shunts are commonly used in the treatment of congenital heart disease that restricts pulmonary blood flow. Such procedures are usually temporary stages which serve until the child is sufficiently large and stable to undergo a more radical but curative procedure. The timing of the curative surgery is critical to the long-term survival of the child. If the procedure is done too soon, mortality is greater because of the size of the infant. However, if the procedure is delayed, irreversible pulmonary hypertension may have developed. Therefore, continuous assessment of pulmonary pressure is critical for the optimum clinical staging of these infants. Unfortunately, because many of these infants have pulmonary atresia or severe stenosis, evaluation of pulmonary arterial pressure by catheter is nearly impossible. Therefore it is of great value to noninvasively estimate the pressure gradient (PG) across AP shunts, which can be used to calculate pulmonary pressure directly by subtraction from the easily measured systemic pressure. Continuous wave Doppler ultrasound is sometimes used to estimate the PG across AP shunts using the simplified Bernoulli equation (PG=4v2). However, this equation has been shown by previous in vitro work in our lab to be inadequate, due to frictional losses across the shunt and pressure recovery distal to the shunt. Using FIDAP 7.52, a finite element computational fluid dynamics package available on the Cray C90 at the Pittsburgh Supercomputing Center, we hope to gain an understanding of discrepancies produced by the simplified Bernoulli equation and use this knowledge to derive a more accurate estimation technique. We have developed a three dimensional mesh which sufficiently describes the region and will use steady and pulsatile computations mesh which sufficiently describes the region and will use steady and pulsatile computations using a turbulent model to deduce the origin and magnitude of the pressure drop across AP shunts of various diameters, lengths and aspects ratios (shunt diameter to pulmonary artery diameter). This proposal requests service units to generate pilot data for a larger proposal.